Composite Rotor System Using Two Race Track Style Cantilevered Yokes

ABSTRACT

A hub system comprises at least one yoke, at least one shear bearing, and at least one mast adapter. The at least one mast adapter is configured to support the at least one yoke and the at least one shear bearing, and the at least one yoke has a flapping hinge that is non-coincident with a flapping hinge of the at least one shear bearing. Another hub system comprises a stacked yoke and a mast adapter. The mast adapter is configured to transfer rotation from a rotor mast to the hub system to rotate the hub system about a central axis of rotation. The mast adapter is further configured to support the stacked yoke such that each yoke in the stacked yoke is configured to accommodate at least some amount of rotation about an axis that is perpendicular to or about perpendicular to the central axis of rotation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a divisional patentapplication of U.S. patent application Ser. No. 15/362,424 filed on Nov.28, 2016, which is a divisional of Ser. No. 13/801,733 filed on Mar. 13,2013, now U.S. Pat. No. 9,505,490, which is hereby incorporated byreference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

When a helicopter hovers, each of the blades is moving at the same speedrelative to the air (i.e., each blade has the same air speed). Thus,each blade generates the same amount of lift. However, as a helicoptermoves, the helicopter blade or blades that are moving in the samedirection as the helicopter movement (i.e., the advancing blades)experience a greater air speed, and the helicopter blade or blades thatare moving in the opposite direction as the helicopter movement (i.e.,the retreating blades) experience a lower air speed. In such a case, theadvancing blades generate more lift and flap up relative to their hoverpositions, and the retreating blades generate less lift and flap downrelative to their hover positions. This results in a phenomenon known asdissymmetry of lift where the advancing blades generate more lift thanthe retreating blades.

To compensate for dissymmetry of lift and provide a stable helicopter,helicopter rotors are commonly designed to accommodate at least someamount of up and down flapping motion while changing the angle of attackfor each of the blades. For instance, a helicopter rotor can be designedto decrease the angle of attack of an advancing blade as it flaps uprelative to its hover position, thereby decreasing the amount of liftthat is generated. Similarly, the helicopter rotor can be designed toincrease the angle of attack of a retreating blade as it flaps downrelative to its hover position, thereby increasing the amount of liftthat is generated. Accordingly, the combination of flapping and changingthe angles of attack of the blades can be used to balance the liftgenerated by each of the blades.

SUMMARY

In some embodiments of the disclosure, a hub system is provided thatcomprises at least one yoke, at least one shear bearing, and at leastone mast adapter. The at least one mast adapter is configured to supportthe at least one yoke and the at least one shear bearing, and the atleast one yoke has a flapping hinge that is non-coincident with aflapping hinge of the at least one shear bearing.

In other embodiments of the disclosure, a hub system is provided thatcomprises a stacked yoke and a mast adapter. The mast adapter isconfigured to transfer rotation from a rotor mast to the hub system torotate the hub system about a central axis of rotation. The mast adapteris further configured to attach to and support the stacked yoke suchthat each yoke in the stacked yoke is configured to accommodate at leastsome amount of rotation about an axis that is perpendicular to or aboutperpendicular to the central axis of rotation.

In yet other embodiments of the disclosure, a hub system is providedthat comprises a mast adapter, a stacked yoke, and a spring mechanism.The mast adapter is configured to support the stacked yoke and thespring mechanism. The mast adapter is further configured to restrain thestacked yoke in in-plane and out-of-plane directions, and the springmechanism is configured to control a bent shape of yokes in the stackedyoke.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosure and the advantagesthereof, reference is now made to the following brief description, takenin connection with the accompanying drawings and detailed description:

FIG. 1 is a perspective view of a helicopter according to an embodimentof the disclosure;

FIG. 2 is a perspective view of a power train according to an embodimentof the disclosure;

FIG. 3 is a cross-sectional view of a main rotor assembly according toan embodiment of the disclosure;

FIG. 4 is a perspective view of a composite rotor system according to anembodiment of the disclosure;

FIG. 5 is a perspective view of a yoke according to an embodiment of thedisclosure;

FIG. 6 is a perspective view of a single mast adapter according to anembodiment of the disclosure;

FIG. 7 is a schematic diagram of flapping angles according to anembodiment of the disclosure;

FIG. 8 is a cross-sectional view of damper mounts according to anembodiment of the disclosure;

FIG. 9 is a flowchart illustrating a method for enhancing the flappingof rotor blades according to an embodiment of the disclosure;

FIG. 10 is a perspective view of a composite rotor system havingI-shaped arms according to an embodiment of the disclosure;

FIG. 11 is a perspective view of a composite rotor system havingI-shaped arms and damper mounts according to an embodiment of thedisclosure;

FIG. 12 is a perspective view of a composite rotor system havingV-shaped arms according to an embodiment of the disclosure;

FIG. 13A is a perspective view of a composite rotor system havingcomposite plate leaf springs according to an embodiment of thedisclosure;

FIG. 13B is a top down view of a middle plate that may be used in thecomposite rotor system of FIG. 13A according to an embodiment of thedisclosure;

FIG. 14 is a perspective view of a composite rotor system havingelastomeric bearing leaf springs according to an embodiment of thedisclosure;

FIG. 15 is a side perspective view of a composite rotor system havingyoke base plates according to an embodiment of the disclosure;

FIG. 16 is a top perspective view of the composite rotor system of FIG.15 according to an embodiment of the disclosure;

FIG. 17 is a bottom perspective view of the composite rotor system ofFIGS. 15-16 according to an embodiment of the disclosure; and

FIG. 18 is a perspective view of a rotor system according to anembodiment of the disclosure.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the implementations, drawings, andtechniques illustrated below, including the exemplary designs andimplementations illustrated and described herein, but may be modifiedwithin the scope of the appended claims along with their full scope ofequivalents.

Certain embodiments of the disclosure include a composite rotor systemthat uses two race track style cantilevered yokes. In at least somecircumstances, the composite rotor system may increase the flappingangles of a rotor blade. For instance, in one particular embodiment, forillustration purposes only and not by limitation, a composite rotorsystem includes two race track style cantilevered yokes that aredisposed between and supported by two cruciform mast adapters. The twocruciform mast adapters only have a limited amount of contact or nocontact with the yoke flexure sections, which results in the yokeflexure sections being able to accommodate a greater amount of flapping.The increased flapping ability can be advantageous in that it allows foran extension of the flight envelope. For example, the increased flappingability may be able to accommodate a greater range of gross weights,center of gravity locations, maneuverability, top speeds, etc.Additionally, at least certain embodiments of the disclosure may also beadvantageous in that they have lower weights and require fewercomponents than other rotor systems. These and other features andadvantages of embodiments are described in greater detail below andshown in the accompanying figures.

FIG. 1 is a perspective view of a helicopter 100. Certain embodiments ofthe disclosure may be used with a helicopter such as helicopter 100.However, it should be understood that the helicopter example is givenmerely for illustration purposes only. Embodiments of the presentdisclosure are not limited to any particular setting or application, andembodiments can be used with a rotor system in any setting orapplication such as with other aircraft, vehicles, or equipment.

Helicopter 100 includes a main rotor assembly 110, a tail rotor assembly120, a fuselage 130, and landing gear 140. Main rotor assembly 110includes two or more blades 112 that are rotated about an axis ofrotation 114 in either a clockwise direction or a counterclockwisedirection as indicated by arrow 116. Main rotor assembly 110 generates alift force that supports the weight of helicopter 100 and a thrust forcethat counteracts aerodynamic drag. Main rotor assembly 110 can also beused to induce pitch and roll of helicopter 100.

Tail rotor assembly 120 includes two or more blades 122 that are rotatedabout an axis of rotation 124 in either a clockwise direction or acounterclockwise direction as indicated by arrow 126. Tail rotorassembly 120 counters the torque effect created by main rotor assembly110 and allows a pilot to control the yaw of helicopter 100.

Fuselage 130 is the main body section of helicopter 100. Fuselage 130optionally holds the crew, passengers, and/or cargo and houses theengine, transmission, gear boxes, drive shafts, control systems, etc.that are needed to establish an operable helicopter. Landing gear 140 isattached to fuselage 130 and supports helicopter 100 on the ground andallows it to take off and land.

FIG. 2 is a perspective view of a power train 200. Power train 200 canbe used in a helicopter such as helicopter 100 shown in FIG. 1. However,power train 200 is not limited to any particular setting. Additionally,it should be noted that the particular example shown in FIG. 2 shows asoft-in plane rotor system having four blades 112. Embodiments of thedisclosure are not limited to any particular configuration of rotorsystem and blades, and embodiments may include any type of rotor system(e.g., fully articulated, rigid, semirigid, etc.) and may include anynumber of blades (e.g., 2, 3, 4, 5, 6, etc.).

Power train 200 includes a transmission 202 that receives power from anengine (not shown) through a driveshaft 204. Transmission 202 drivesaccessories and controls the rotation as indicated by arrow 116 of mast206 about an axis of rotation 114. Mast 206 transfers its rotationalmovement to blades 112 through a hub 208 that connects mast 206 toblades 112.

Hub 208 optionally includes one or more flexible yokes 210 that enableblades 112 to flap up in the direction indicated by arrow 212 and flapdown in the direction indicated by arrow 214. Hub 208 may also include amain rotor grip 216 for each blade 112 that is attached to hub 208. Mainrotor grip 216 includes an outboard end that attaches to a blade 112, aninboard end that attaches to a pitch horn 218, and a spindle between theoutboard end and the inboard end. The spindle is supported by a shearbearing 220 that holds the spindle in place and allows it to rotate.Shear bearing 220 is in turn held in place by a bridge plate 222 thatattaches shear bearing 220 to yoke 210.

Each pitch horn 218 is connected to a pitch linkage 224. Each pitchlinkage 224 is driven up and down (e.g., in the directions shown byarrows 212 and 214) by a swashplate assembly 226. Accordingly, asswashplate assembly 226 moves, it drives pitch linkage 224, which drivespitch horn 218 which rotates main rotor grip 216 about shear bearing220. This allows the pitch of each of the blades 112 to be controlled.For instance, each blade 112 is able to rotate clockwise orcounterclockwise as indicated by arrow 228 about an axis of rotation 230that runs along the length of each blade 112.

FIG. 3 is a cross-sectional view of one blade 112 of main rotor assembly110. Main rotor assembly 110 includes a top yoke 302 and a bottom yoke304 that are disposed between and supported by a top mast adapter 306and a bottom mast adapter 308. Top mast adapter 306 and/or bottom mastadapter 308 may translate rotational movement from mast 206 to the othercomponents of rotor assembly 110.

Blade 112 is attached to yoke 304 through a main rotor grip 216. Anoutboard section of main rotor grip 216 includes one or more apertures314 or other attachment mechanisms that attach to blade 112. The mainrotor grip 216 is attached to yoke 304 through a centrifugal force (CF)bearing 316 and a CF fitting 318. CF bearing 316 optionally allows blade112 to articulate relative to yoke 304. For instance, CF bearing 316 mayallow blade 112 to flap up in the direction indicated by arrow 212 andflap down in the direction indicated by arrow 214. Also for instance, CFbearing 316 may allow relative motion between main rotor grip 216 andyoke 304.

An inboard section of main rotor grip 216 may include a spindle thatfits within a shear bearing 220. Shear bearing 220 in combination withCF bearing 316 allows main rotor grip 216 to rotate such that the angleof attack of blade 112 can be changed. Shear bearing 220 is disposedbetween two lead/lag dampers 326, and shear bearing 220 and lead/lagdampers 326 are held in place and supported by top mast adapter 306 andbottom mast adapter 308.

FIG. 4 is a perspective view of a composite rotor system 400. Rotorsystem 400 may be included in a rotor assembly such as in the rotorassemblies shown in FIGS. 1-3. However, embodiments are not limited toany particular setting or application and can be used in settings andapplications different than the particular examples shown in FIGS. 1-3.

Rotor system 400 includes a top yoke 402 that is stacked upon a bottomyoke 404. The two stacked yokes 402 and 404 are disposed between andheld into place by a top mast adapter 406 and a bottom mast adapter 408.Generally, one yoke supports two rotor blades, but other yokearrangements (e.g., triangular) could support additional rotor blades(e.g., three).

Each yoke 402 and 404 is optionally a race track style yoke having anannular shape and is made of a composite material such as, but notlimited to, fiberglass and/or carbon fiber. Additionally, each yoke 402and 404 may have a mast or inboard section 410, an end or outboardsection 412, flexure sections 414 extending between inboard sections 410and outboard sections 412, and a central aperture 416.

Each mast adapter 406 and 408 is optionally a cruciform mast adapterhaving a central aperture 418 that is configured to accommodate a mastand four arms 420 extending outward from central aperture 418.Additionally, each arm 420 may include one or more apertures 422 orother attachment mechanisms for attaching mast adapters 406, 408 andyokes 402, 404 together. Mast adapters 406 and 408 may be made of arigid material such as a metal (e.g., steel). The rigid materialillustratively restricts out-of-plane movement and in-plane torsionalmovement (e.g., the rigid material restricts relatively all torsionaldeflections). Mast adapters 406 and 408 are not however limited to anyparticular material and may be made of other materials as well.

In an embodiment, yoke flexure sections 414 are configured to flap upand down in the directions indicated by arrow 424. As can be seen inFIG. 4, neither mast adapter 406 nor mast adapter 408 obstructs anyportion of flexure sections 414 in the flapping directions as indicatedby arrow 424. Instead, each mast adapter arm 420 connects to one yokeinboard section 410 and fits within the central aperture 416 of theother yoke. In at least certain circumstances, this increases a lengthof the yoke that can flap without increasing an overall length of theyokes 402 and 404. Since the yoke can flex a certain amount per unitlength and the length of the yoke that can flap is increased, yokeoutboard sections 412 are able to flap to greater angles.

FIG. 5 is a perspective view of yoke 402 from FIG. 4 by itself. In anembodiment, yokes 402 and 404 in FIG. 4 may be the same or approximatelythe same. However, yokes 402 and 404 could be configured differentlyfrom each other.

As previously mentioned, yoke 402 includes mast or inboard sections 410,outboard sections 412, flexure sections 414, and aperture 416.Additionally, FIG. 5 shows that inboard sections 410 may have one ormore apertures 501 or other attachment mechanisms for attaching yoke 402to another yoke and/or mast adapters 406 and 408 (shown and labeled inFIG. 4). Furthermore, FIG. 5 shows that inboard sections 410 have alength 502, that flexure sections 414 have lengths 504, that yoke 402has an overall length 506, that inboard sections 410 and outboardsections 412 have a thickness 508, that flexure sections 414 have athickness 510, and that aperture 416 has a width 512.

In an embodiment, the flexure section thickness 510 is less than theinboard and outboard section thickness 508. This enables flexuresections 414 to be relatively flexible and be able to flap, while theinboard sections 410 and outboard sections 412 are relatively rigid suchthat they can support secure attachments to a mast, main rotor grip,etc. Additionally, as previously noted, the design of the rotor systemin at least certain embodiments enables the flexure section length 504to be relatively long compared to the yoke overall length 506 enablingyoke 402 to achieve greater flapping angles.

FIG. 6 is a perspective view of mast adapter 406 from FIG. 4 by itself.In an embodiment, mast adapters 406 and 408 in FIG. 4 may be the same orapproximately the same. However, mast adapters 406 and 408 could beconfigured differently from each other.

Mast adapter 406 includes a central aperture 418, arms 420, and armapertures 422. In the particular 4-bladed embodiment shown in FIG. 6,mast adapter 406 includes four arms 420 (e.g., one arm 420 for eachblade). However, embodiments are not limited to any number of arms 420and can include any number or arms 420 depending on the number ofblades. In one embodiment, each arm has a width 602, and arm width 602is approximately the same or less than the yoke mast or inboard sectionlength 502 (shown and labeled in FIG. 5) such that arms 420 do notextend into the yoke flexure sections 414 (shown and labeled in FIGS.4-5). Furthermore, each arm width 602 is less than yoke aperture width512 (shown and labeled in FIG. 5) such that arms 420 fit within yokeapertures 416 (shown and labeled in FIGS. 4-5). These relativedimensions enable mast adapter 406 to be able to support yokes withoutinterfering with yoke flapping.

Additionally, FIG. 6 shows that mast adapter arms 420 may include twosets of opposing arms that are perpendicular or approximatelyperpendicular to each other for a 4-bladed rotor system. In anembodiment, the first set of opposing arms lie within a first plane at afirst level 604, and the second set of opposing arms lie within a secondplane at a second level 606. First level 604 and second level 606 areoptionally parallel and are offset in a vertical direction 608. Thisenables mast adapter arms 420 to be able to contact and attach to twostacked yokes that are at different levels.

FIG. 7 is a schematic diagram of flapping angles according to anembodiment of the disclosure. Line 702 represents the axis of rotationof a mast (e.g., axis of rotation 114 in FIG. 1), and line 704 isperpendicular to line 702. Line 704 represents the position of the rotorhub assembly, and the various lines in FIG. 7 show the flapping anglesand positions relative to line 704. Line 706 represents a precone orinitial position of a yoke and is at an angle θ₁ with respect to line704. Point 708 represents a yoke virtual hinge point, which may be asingle point or a range of locations simplified to a single point forthe purpose of flapping analysis. Line 710 represents a tangency to theoutboard end of the flapped portion of the yoke (e.g., the flexuresection). Line 710 is at an angle θ₂ with respect to line 706. Point 712represents a flapping or hinge point of a rotor blade (e.g., a CFbearing), and line 714 represents the actual rotor blade flappingposition. Line 714 passes through point 716. Point 716 represents theshear bearing pivot point, which is fixed in position relative to lines702 and 704. Line 714 is at an angle θ₃ with respect to line 710. Thetotal flapping angle of the blade relative to the precone position isthe sum of θ₂ and θ₃ which is θ₄. In some cases, θ₂ is approximately4.5°, θ₃ is approximately 1.5°, and θ₄ is approximately 6.0°. However,embodiments are not limited to any specific flapping angles.

In at least some embodiments of the disclosure, the yoke virtual hingepoint 708 is located closer to the mast axis of rotation 702 as comparedto rotor systems having different designs (e.g., the yoke virtual hingepoint 708 is located between the blade flapping point 712 and the mast702). For instance, the yoke virtual hinge 708 may be located at station2.0 which is 2 inches away from the center of the mast. This extends theflapped yoke length 710 which increases the total flapping angle θ₄. Inrotor systems having different designs, the yoke hinge point 708 may befurther outboard. For example, in at least some other rotor systems, theyoke hinge point 708 may coincide with the blade flapping point 716,which results in a reduced amount of flapping (e.g., θ₄ is not greaterthan θ₂). Accordingly, embodiments of the disclosure can be advantageousin being able to provide a greater blade flapping angle θ₄.

FIG. 8 is a side cross-sectional view of damper mounts 802 that mayoptionally be included within a rotor system. In an embodiment, dampermounts 802 are integrally formed with mast adapters 406 and 408. Forinstance, one damper mount 802 may extend from each of the arms of amast adapter (e.g., from each of mast adapter arms 420 in FIGS. 4 and6). Damper mounts 802 are configured to secure lead/lag dampers 326 inplace, which in turn support a shear bearing 220. Damper mounts 802 canfit within an aperture (e.g., aperture 416 in FIGS. 4-5) of a yoke 404,thus damper mounts 802 can be included within mast adapters 406 and 408without obstructing the yoke flapping.

FIG. 9 is a flowchart illustrating a method 900 of enhancing flapping ofrotor blades. At block 902, a length of a yoke flexure section and alength of a yoke mast section are determined. At block 904, a size of amast adapter arm is selected such that the mast adapter arm supports theyoke mast section and does not extend into the yoke flexure section. Atblock 906, a material and/or a shape for the mast adapter is selected.The material and/or shape may be selected such that the mast adapterlimits out-of-plane, in-plane, and torsional movement. The materialand/or shape may also be selected to eliminate “potato chipping” and/orcontrol interlaminar shear (ILS) stress in the yokes. At block 908, theyoke and mast adapter are designed such that the yoke is configured toflap at a point inboard of a shear bearing (e.g., a flapping point orvirtual hinge that is located between a shearing bearing and a mastsection of the flexible yoke). Then, at block 910, instructions areprovided to assemble and/or operate a rotor system. For instance, theinstructions may include instructions to attach a rotor blade to a bladegripping bearing, attach the blade gripping bearing to an outboard endof a flexible yoke, and attach a mast section of the flexible yoke to amast adapter. The instructions for operating the rotor system mayinclude instructions to flap the flexible yoke at an inboard flappingpoint that enables the rotor blade to flap to a greater angle (e.g., agreater angle θ₄ in FIG. 7).

FIG. 10 is a perspective view of a composite rotor system 1000. Similarto composite rotor system 400 in FIG. 4, composite rotor system 1000also includes a top yoke 1002, a bottom yoke 1004, a top mast adapter1006, a bottom mast adapter 1008, and mast adapter arms 1020. However,as can be seen in FIG. 10, mast adapter arms 1020 have an I-shapedcross-sectional shape instead of the rectangular cross-sectional shapeshown in FIG. 4. In particular, each mast adapter arm 1020 includes aninner flange 1021, an outer flange 1022, and a web 1023. Each innerflange 1021 is configured to attach to and support a mast section of oneof the yokes 1002 or 1004. Each web 1023 connects inner flange 1021 toouter flange 1022, and each outer flange 1022 is connected to a mastsleeve 1030 that is configured to accommodate a mast (e.g., mast sleeve1030 may have a splined inner surface that is configured to attachcomposite rotor system 1000 to a rotor mast).

In an embodiment, each inner flange 1021 has an inboard section 1024that is not connected to any other portion of a mast adapter 1006 or1008. This feature, in combination with the I-shaped cross-sectionalshape, may enable mast adapters 1006 and 1008 to accommodate a greateramount of flapping. For instance, in FIG. 10, the inner flanges 1021 oftop mast adapter 1006 and bottom mast adapter 1008 that are attached totop yoke 1002 are able to rotate (e.g., pivot) about axis of rotation1040 in the directions indicated by arrow 1042. This enables top yoke1002 to be able to flap to a greater angle. Bottom yoke 1004 issimilarly disposed between and supported by inner flanges 1021 thatenable the bottom yoke 1004 to potentially flap to a greater angle. Inone particular example, the I-shaped arms 1020 enable a yoke to flap anextra 1° as compared to the rectangular shaped arms 420 in FIG. 4.However, embodiments are not limited to any particular angles.Furthermore, the I-shaped arms 1020 may also be beneficial in reducingILS stress in the yokes 1002 and 1004. For instance, thepivoting/rotating inner flanges 1021 allow for out-of-plane deflectionsthat absorb some of the stress that would normally go into the yoke.

FIG. 11 is a perspective view of a composite rotor system 1100. Similarto composite rotor system 1000 in FIG. 10, composite rotor system 1100also includes I-shaped mast adapter arms 1120. From the view shown inFIG. 10, only one mast adapter 1106 is visible. However, it should benoted that in an embodiment that rotor system 1100 includes both a topand a bottom mast adapter similar to the configurations shown in FIGS. 4and 10.

Each mast adapter 1106 includes a number of I-shaped arms 1120. Each armincludes an inner flange 1121, an outer flange 1122, and a web (hiddenin FIG. 11) that connects inner flange 1121 and outer flange 1122. Eachinner flange 1121 is configured to attach to and support a yoke 1102 or1004. Additionally, each inner flange 1121 has an inboard section 1124that is not connected to any other portion of mast adapter 1106.Accordingly, inner flanges 1121 are able to pivot/rotate similarly toinner flanges 1021 in FIG. 10, which enables yokes 1102 and 1104 to flapto potentially greater angles.

As can be seen in a comparison of FIGS. 10 and 11, mast adapters 1006and 1008 in FIG. 10 have a cruciform shape while mast adapter 1106 inFIG. 11 has a roughly diamond or star shape. This shows that embodimentsof the disclosure are not limited to any particular shape orconfiguration and that embodiments can be implemented in a number ofdifferent fashions.

Additionally, mast adapter 1106 in FIG. 11 shows one potential method ofsupporting damper mounts 1130. In particular, the outboard end of eachmast adapter arm 1120 can be configured to attach to and support adamper mount 1130. Alternatively, damper mounts 1130 could be integrallyformed with mast adapter arms 1120 such that at least a portion ofdamper mounts 1130 and mast adapter arms 1120 are made from a same pieceof material. Furthermore, it should be noted that the damper mountconfiguration shown in FIG. 11 is designed to not obstruct yokeflapping. Accordingly, damper mounts 1130 can optionally be includedwithin composite rotor systems of the present disclosure withoutinterfering with yoke flapping.

FIG. 12 is a perspective view of a composite rotor system 1200.Composite rotor system 1200 functions similarly to composite rotorsystems 1000 in FIGS. 10 and 1100 in FIG. 11. However, instead of usingI-shaped arms to support yokes, composite rotor system 1200 usesV-shaped arms 1220 to support yokes 1202 and 1204. It should also benoted that similar to FIG. 10, the view shown in FIG. 11 only shows onemast adapter 1206. Embodiments of composite rotor system 1200illustratively include both a top and a bottom mast adapter. Also, itshould be noted that FIG. 11 shows that composite rotor system 1100 onlycontains I-shaped arms and that FIG. 12 shows that composite rotorsystem 1200 only contains V-shaped arms, that embodiments are notlimited to only having I-shaped or V-shaped arms. In other embodiments,a composite rotor system may include a combination of I-shaped andV-shaped arms, may have other shaped arms (e.g., not I-shaped orV-shaped), or may have any combination of I-shaped, V-shaped, and othershaped arms.

Each V-shaped arm 1220 includes two top portions 1222, a bottom portion1224, and sidewalls connecting the top portions 1222 and the bottomportion 1224. Top portions 1222 are configured to be attached to andsupported by a support plate 1226 of mast adapter 1206. In theparticular example shown in FIG. 12, support plate 1226 and V-shapedarms 1220 are separate pieces. However, in another embodiment, supportplate 1226 and V-shaped arms 1220 may be integrally formed as one piece.In an embodiment where support plate 1226 and V-shaped arms 1220 areformed as one piece, support plate 1226 and V-shaped arms 1220 may bemade from a metal (e.g., 6Al-4V titanium alloy). In an embodiment wheresupport plate 1226 and V-shaped arms 1220 are formed as separate pieces,support plate 1226 may be made of a metal (e.g., 6Al-4V titanium allow),and V-shaped arms 1220 may be made of a composite material (e.g.,fiberglass, carbon fiber, or IM7/8552 carbon/epoxy laminate).Embodiments are not however limited to any particular configuration ormaterials.

In composite rotor system 1200, a mast or center section of each yoke1202 and 1204 is disposed between and supported by two V bottom portions1224. Bottom portions 1224 are configured to rotate or pivot the same orsimilarly to how the inner flanges 1021 and 1121 of the I-shaped arms inFIGS. 10 and 11 are configured to rotate or pivot. This allows yokes1202 and 1204 to flap to greater angles and also possibly absorb some ofthe ILS stress in yokes 1202 and 1204. Furthermore, it should be notedthat the V bottom portions 1224 may have one or more apertures or otherattachment mechanisms 1225 that are configured to attach to the centeror about the center of yokes 1202 and 1204 (e.g., apertures 1225 thatconnect to station 0.0 of yokes 1202 and 1204). This may be useful inpreventing or reducing delamination of yokes 1202 and 1204. Forinstance, in at least certain circumstance, the center of the yoke(e.g., station 0.0) may have less stress than portions of the yokefurther away from the center. Accordingly, by being able to putattachment holes/apertures in the center of the yoke, the attachmentholes/apertures experience less stress and are less likely todelaminate. This may reduce maintenance time and costs associated withhaving to repair or replace yokes because of delamination issues.

FIG. 12 further shows that the V-shaped composite rotor system 1200 canalso be configured to support damper mounts 1230. Again, damper mounts1230 can be configured to be attached to and supported by mast adapter1206 or can be integrally formed with mast adapter 1206. Also, dampermounts 1230 may be integrated within composite rotor system 1200 suchthat they do not obstruct yoke flapping.

FIG. 13A is a perspective view of a composite rotor system 1300.Composite rotor system 1300 includes a top yoke 1302, a bottom yoke1304, a top mast adapter 1306, a bottom mast adapter 1308, four leafsprings 1340, and a middle plate 1350. In an embodiment, middle plate1350 is placed in between top yoke 1302 and bottom yoke 1304. Then, asis shown in FIG. 13A, leaf springs 1340 are placed on the sides of yokes1302 and 1304 opposite middle plate 1350. The yokes 1302, 1304, mastadapters 1306, 1308, leaf springs 1340, and middle plate 1350 are thenconnected or attached together by using through bolts or otherattachment mechanisms 1321 that are placed through apertures in arms1320 of the mast adapters 1306, 1308, yokes 1302, 1304, and middle plate1350.

In an embodiment, leaf springs 1340 and/or middle plate 1350 arerectangularly shaped plates made of a composite material (e.g.,fiberglass or carbon fiber). However, embodiments of leaf springs 1340and middle plate 1350 are not limited to any particular shapes ormaterials.

In at least some circumstances, leaf springs 1340 and middle plate 1350may be able to increase flapping angles by creating an additional pivotpoint or hinge point that enables greater yoke flapping. For instance,as shown in FIG. 13A, leaf springs 1340 and middle plate 1350 divideeach yoke 1302 and 1304 into three different sections 1342, 1344, and1346. In section 1342, each yoke 1302 or 1304 is supported by a mastadapter arm 1320, a leaf spring 1340, and middle plate 1350. In section1344, each yoke 1302 or 1304 is supported only by a leaf spring 1340 andmiddle plate 1350. In section 1346, each yoke 1302 and 1304 is notsupported by a mast adapter arm 1320, a leaf spring 1340, or middleplate 1350.

Yoke section 1342 is essentially held firmly in place and is not able toflap because it is being constrained by a mast adapter arm 1320 andmiddle plate 1350. Then, as the yoke 1302 or 1304 reaches section 1344,yoke 1302 or 1304 is able to flap because it is only being supported bya leaf spring 1340 and middle plate 1350. In particular, yoke 1302 or1304 will have a pivot point or a hinge point 1343 between sections 1342and 1344. Yoke section 1344 is able to flap up or down about pivot pointor hinge point 1343. Then, as the yoke 1302 or 1304 reaches section1346, yoke 1302 or 1304 is able to flap an additional amount because itis not supported by a leaf spring 1340, a mast adapter arm 1320, ormiddle plate 1350. In particular, yoke 1302 or 1304 will have anotherpivot point or hinge point 1345 between sections 1344 and 1346. Yokesection 1346 is able to flap up or down about pivot point or hinge point1345. Accordingly, instead of a yoke in a composite rotor system onlyhaving one pivot point or hinge point, the use of leaf springs 1340 andmiddle plate 1350 enables a yoke to have two pivot points or hingepoints (e.g., points 1343 and 1345) that enable the yoke to flap to agreater flapping angle. Additionally, embodiments of leaf springs 1340and middle plate 1350 may also be beneficial in reducing the intensityof strains at any particular location of a yoke by more evenlydistributing the strain throughout a larger portion of the yoke.

FIG. 13B is a top down view of middle plate 1350 from FIG. 13A byitself. As previously mentioned, middle plate 1350 is optionally placedbetween a pair of stacked yokes (e.g., yokes 1302 and 1304 in FIG. 13A).As shown in FIG. 13B, middle plate 1350 may have a rectangular shape.However embodiments are not limited to any particular shape, and middleplate 1350 could have a shape or configuration different than thespecific example shown in FIG. 13B. Additionally, middle plate 1350 mayinclude a number of apertures or other attachment mechanisms such thatmiddle plate 1350 can be connected to or attached to yokes (e.g., yokes1302 and 1304 in FIG. 13A) and/or mast adapter arms (e.g., mast adapterarms 1320 in FIG. 13A). In the particular example, shown in FIG. 13B,middle plate 1350 includes a central aperture 1351 configured toaccommodate a rotor mast, a first set of opposing apertures 1352configured to attach to a first yoke, and a second set of opposingapertures 1353 configured to attach to a second yoke. Each group ofapertures in the sets of opposing apertures 1352 and 1353 may includethree apertures arranged in a triangular manner as is shown in FIG. 13B.However, embodiments are not limited to any particular number orconfiguration of apertures, and embodiments can include differentnumbers of apertures and different configurations of apertures.

FIG. 14 is a perspective view of a composite rotor system 1400.Composite rotor system 1400 is in some aspects similar to compositerotor system 1300 in FIG. 13. However, in composite rotor system 1400,elastomeric bearings 1430 are used as leaf springs instead of acomposite plate 1340. It should be noted that embodiments of thedisclosure are not limited to only the elastomeric bearing and compositeplate spring mechanisms shown in FIGS. 13-14. In other embodiments,spring mechanisms may include coil, torsional, flexure, or other typesof mechanisms for applying spring force to control a bent shape of ayoke.

Similar to composite rotor system 1300 in FIG. 13, the yokes 1402 and1404 are divided into three sections 1442, 1444, and 1446. In section1442, each yoke 1402 or 1404 is disposed between and held in place byopposing mast adapter arms 1420. Accordingly, yokes 1402 and 1404 areessentially not able to flap in section 1442 because they are beingconstrained by the mast adapter arms 1420. Then, as the yoke 1402 or1404 reaches section 1444, yokes 1402 and 1404 are supported by opposingelastomeric bearings 1430. Elastomeric bearings 1430 optionally includeone or more layers made of an elastomeric material (e.g., rubber)interleaved by one or more layers made of a rigid material (e.g., ametal). Elastomeric bearings 1430 provide some support for yokes 1402and 1404 in section 1444, but also permit flapping. Accordingly, yokesection 1444 will have a pivot point or a hinge point 1443 betweensections 1442 and 1444. Also, it should be noted that in someembodiments, there may be a gap 1450 between where the mast adapter arms1420 end and where the elastomeric bearings 1430 are positioned.Additionally, there may be a gap between the mast adapter arms 1420 andthe yokes 1402 and 1404. In particular, the mast adapter arms 1420 arenever in direct contact with yokes 1402 or 1404. Instead, the mastadapter arms 1420 clamp onto an adapter 1410 at the inboard end of thearms 1420. Adapter 1410 in turn clamps the yokes 1402, 1404 and alsoclamps the elastomeric bearings 1430 to the yokes 1402 and 1404.

In an embodiment, the pivot point or hinge point 1443 may occur withinthe gap 1450 between where the mast adapter arms 1420 end and where theelastomeric bearings 1430 are positioned. Then, as the yoke 1402 or 1404reaches section 1446, yokes 1402 and 1404 are not supported by eithermast adapter arms 1420 or elastomeric bearings 1430. Accordingly, insection 1446, yokes 1402 and 1404 are able to flap an additional amountbecause they are not supported by either mast adapter arms 1420 orelastomeric bearings 1430. In particular, another pivot point or hingepoint 1445 is created where the elastomeric bearings 1430 end, and yokesection 1446 is able to flap about point 1445. Accordingly, similar tothe embodiment in FIG. 13, composite rotor system 1400 in FIG. 14 mayhave two pivot points or hinge points (e.g., points 1443 and 1445) thatenable greater yoke flapping. Also, the use of different yoke regionsmay again help reduce the intensity of strains in a yoke by more evenlydistributing the stresses through a larger portion of the yoke.

FIG. 15 is a side perspective view of a composite rotor system 1500.Composite rotor system 1500 is in some aspects similar to compositerotor system 400 in FIG. 4. However, in composite rotor system 1500, thetop mast adapter 1506 and the bottom mast adapter 1508 are not directlyconnected to the yokes (e.g., yoke 1502). Instead, top mast adapter 1506and bottom mast adapter 1508 are indirectly connected to the yokesthrough yoke base plates 1550.

In one embodiment, composite rotor system 1500 includes a drive hub 1552that is illustratively directly connected to a rotor mast and transfersrotational movement from the rotor mast to the rest of the components ofcomposite rotor system 1500. Drive hub 1552 can be a single-piece drivehub or could alternatively comprise multiple pieces. In the particularexample shown in FIG. 15, drive hub 1552 is connected to top mastadapter 1506 and/or bottom mast adapter 1508. However, embodiments arenot limited to any particular configuration of connecting drive hub 1552to the rest of the components of composite rotor system 1500.

Top mast adapter 1506 and bottom mast adapter 1508 each includes one arm1520 for each blade in a rotor system (e.g., 2, 3, 4, 5, 6 arms, etc.).Each arm 1520 is connected to a mast or center section of a yoke 1502through a yoke base plate 1550. In particular, each yoke 1502 is held inplace by an opposing pair of yoke base plates 1550, which are in turnheld in place by top mast adapter 1506 and bottom mast adapter 1508.Additionally, it should be noted that each yoke base plate 1550 may beabout the same size as the yoke mast or center sections (e.g., yokesection 502 in FIG. 5). This allows for the composite rotor system 1500to not interfere with yoke flapping and also enables a yoke flappingpoint or virtual hinge point to be at a point that is further inboard ascompared to other designs (e.g., the yoke flapping or virtual hingepoint may be located between the mast and a shear bearing). In at leastcertain circumstances, this may enable composite rotor system 1500 toprovide for increased flapping angles.

FIG. 16 is a top perspective view of composite rotor system 1500 fromFIG. 15. FIG. 16 shows that in one embodiment that top mast adapter 1506has a diamond shape with the arms 1520 being located at the ends of thediamond points. However, embodiments are not limited to any particularshapes and top mast adapter 1506, as well as bottom mast adapter 1508(shown in FIGS. 15 and 17), may have any shape. Furthermore, FIG. 16shows that each mast adapter arm 1520 has two apertures or otherattachment mechanisms 1521 that are configured to connect top mastadapter 1506, drive hub 1552 (shown in FIG. 15), yokes 1502 and 1504,and bottom mast adapter 1508 (shown in FIGS. 15 and 17) together. In oneembodiment, such as in the example shown in FIGS. 15-17, the attachmentmechanisms are positioned at station 0.0 (e.g., the center) of the yokes1502 and 1504. In at least certain circumstances, station 0.0 of yokes1502 and 1504 may experience less ILS stress as compared to otherportions of the yoke that are further outboard. Accordingly, by beingable to locate attachment mechanisms 1521 at station 0.0, there may be areduced chance of yoke delamination caused by ILS stress at ahole/aperture in a yoke 1502 or 1504.

FIG. 16 further shows additional components that may optionally beincluded in a composite rotor system 1500. For instance, composite rotorsystem 1500 may include damper mounts 1530, shear bearings 1535, bladegrips 1540, CF bearings 1545, and pitch horns 1555. The damper mounts1530 may be integrally formed with the mast adapters 1506 and 1508 as isshown in FIG. 16, or alternatively, the damper mounts 1530 may beseparate components that are attached to the mast adapters 1506 and1508.

FIG. 17 is a bottom perspective view of composite rotor system 1500 fromFIGS. 15-16. FIG. 17 more clearly shows the bottom mast adapter 1508that was hidden or partially hidden in FIGS. 15-16. As can be seen inFIG. 17, bottom mast adapter 1508 has the same or similar shape as topmast adapter 1506 (shown in FIGS. 15-16). Bottom mast adapter 1508includes a number of arms 1520, and each arm includes two apertures orother attachment mechanisms 1521 configured to connect to and support ayoke at station 0.0. Additionally, bottom mast adapter 1508 may haveintegrally formed or separately attached damper mounts 1530. FIG. 17,also shows other optional components such as, but not limited to, bladegrips 1540, CF bearings 1545, and pitch horns 1555.

FIG. 18 is a perspective view of a rotor assembly 1800 in which one ormore embodiments disclosed in this application can be incorporatedwithin. For instance, the composite rotor systems in FIGS. 4 and 10-17could be used in a rotor assembly such as rotor assembly 1800. However,embodiments are not limited to any particular operating environment andcan be used in systems differing from the particular example shown inFIG. 18.

Rotor assembly 1800 includes a hub 1801 that connects yokes 1802 and1804 to a mast 1806. Hub 1801 optionally includes any one or more of thecomponents shown or described above such as, but not limited to, a topmast adapter, a bottom mast adapter, a drive hub, yoke base plates,composite plate leaf springs, elastomeric bearing leaf springs, integralor separate lead/lag dampers, attachment mechanisms (e.g., attachmentmechanisms to connect to a yoke at station 0.0), I-shaped mast adapterarms, V-shaped mast adapter arms, etc.

Each yoke 1802 and 1804 supports a pair of blade grips 1808, and eachblade grip 1808 supports a rotor blade 1810. Each blade grip 1808 is inturn supported by a shear bearing 1812 and a CF bearing 1814. The bladegrips 1808 are each connected to a pitch horn 1816 that is driven by apitch linkage 1818 that enables blades 1810 to be articulated.

As has been described above and shown in the figures, certainembodiments of the disclosure include a composite rotor system that usestwo race track style cantilevered yokes. In at least some circumstances,the composite rotor system may increase the flapping angles of a rotorblade. This can be accomplished in some instances by using two cruciformmast adapters that have only a limited amount of contact or no contactwith the yoke flexure sections. This increases the length of the yokeflexure sections that can flap which results in the yoke being able toaccommodate a greater amount of flapping. Some embodiments may also beable to increase the flapping angles of a rotor blade by usingadditional features such as, but not limited to, yoke base plates, yokeattachment mechanisms at station 0.0, leaf springs (e.g., compositeplate leaf springs or elastomeric bearing leaf springs), I-shaped mastadapter arms, and/or V-shaped mast adapter arms. Additionally, at leastcertain embodiments of the disclosure may also be advantageous in thatthe composite rotor systems have lower weights and require fewercomponents than other rotor systems. For instance, other rotor systemsmay require more mast adapters and/or other hardware to support astacked yoke.

Finally, it should be noted that at least one embodiment is disclosedand variations, combinations, and/or modifications of the embodiment(s)and/or features of the embodiment(s) made by a person having ordinaryskill in the art are within the scope of the disclosure. Alternativeembodiments that result from combining, integrating, and/or omittingfeatures of the embodiment(s) are also within the scope of thedisclosure. Where numerical ranges or limitations are expressly stated,such express ranges or limitations should be understood to includeiterative ranges or limitations of like magnitude falling within theexpressly stated ranges or limitations (e.g., from about 1 to about 10includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13,etc.). For example, whenever a numerical range with a lower limit,R_(l), and an upper limit, R_(u), is disclosed, any number fallingwithin the range is specifically disclosed. In particular, the followingnumbers within the range are specifically disclosed:R=R_(l)+k*(R_(u)−R_(l)), wherein k is a variable ranging from 1 percentto 100 percent with a 1 percent increment, i.e., k is 1 percent, 2percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent, 51percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98percent, 99 percent, or 100 percent. Unless otherwise stated, the term“about” shall mean plus or minus 10 percent of the subsequent value.Moreover, any numerical range defined by two R numbers as defined in theabove is also specifically disclosed. Use of the term “optionally” withrespect to any element of a claim means that the element is required, oralternatively, the element is not required, both alternatives beingwithin the scope of the claim. Use of broader terms such as comprises,includes, and having should be understood to provide support fornarrower terms such as consisting of, consisting essentially of, andcomprised substantially of Accordingly, the scope of protection is notlimited by the description set out above but is defined by the claimsthat follow, that scope including all equivalents of the subject matterof the claims. Each and every claim is incorporated as furtherdisclosure into the specification and the claims are embodiment(s) ofthe present disclosure.

What is claimed is:
 1. A hub system comprising: a stacked yokecomprising at least a first race-track style yoke and a secondrace-track style yoke; and a mast adapter configured to transferrotation from a rotor mast to the hub system to rotate the hub systemabout a central axis of rotation, and configured to attach to andsupport the stacked yoke such that each yoke in the stacked yoke isconfigured accommodate at least some amount of rotation about an axisthat is perpendicular to or about perpendicular to the central axis ofrotation.
 2. The hub system of claim 1, wherein the mast adaptercomprises apertures in a cruciform pattern, and wherein the aperturesare configured to connect to a center or about the center of a mastsection of each yoke in the stacked yoke.
 3. The hub system of claim 1,wherein the mast adapter comprises an outer plate and an inner plate,wherein the inner plate is configured to transfer the rotation from therotor mast to the stacked yoke, and wherein the outer plate isconfigured to control out-of-plane motion and spanwise torsion of thestacked yoke.
 4. The hub system of claim 3, wherein the inner plate isconfigured to absorb shear strain from a flexure section of the stackedyoke to reduce an amount of shear strain in apertures of the stackedyoke.
 5. The hub system of claim 4, wherein the inner plate comprises acomposite material or a metal.
 6. The hub system of claim 1, wherein themast adapter comprises a flexure section that is configured to attach toand support the stacked yoke.
 7. The hub system of claim 6, wherein theflexure section comprises an I-shaped cross-section or a V-shapedcross-section.
 8. The hub system of claim 6, wherein the flexure sectionis integrally formed with the mast adapter, or wherein the flexuresection and the mast adapter comprise separate components.
 9. The hubsystem of claim 3, wherein the inner plate is configured to transfertorque to the at least one yoke, and wherein the outer plate isconfigured to control flapping and feathering of the at least one yoke.10. A hub system comprising: a mast adapter; a stacked yoke comprisingat least a first race-track style yoke and a second race-track styleyoke; a spring mechanism; and wherein the mast adapter is configured tosupport the stacked yoke and the spring mechanism, wherein the mastadapter is configured to restrain the stacked yoke in in-plane andout-of-plane directions, and wherein the spring mechanism is configuredto control a bent shape of yokes in the stacked yoke.
 11. The hub systemof claim 10, wherein the spring mechanism comprises a leaf spring. 12.The hub system of claim 10, wherein the spring mechanism comprises acantilevered plate that is parallel to a yoke arm and that is affixed toa cantilevered support structure that is configured to apply force in aflapping direction.
 13. The hub system of claim 10, wherein the springmechanism is selected from a group consisting of a coil, a torsional, anelastomeric, or a flexure type spring mechanism.
 14. The hub system ofclaim 10, wherein the spring mechanism comprises multiple springmechanisms, and wherein the multiple spring mechanisms are spaced alonga span of a flexure of the stacked yoke to create multiple virtual hingepoints in the stacked yoke.